/Engine/Source/Editor/AnimGraph/Public/AnimPreviewInstance.h
Convert current modified bone transforms (BoneControllers) to transform curves (CurveControllers) it does based on CurrentTime. This function does not set key directly here. It does wait until next update, and it gets the delta of transform before applying curves, and creates curves from it, so you'll need delegate if you'd like to do something after (set with SetKeyCompleteDelegate)
void SetKey()